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A brief introduction to the stabilization mechanism of composite stabilizers

- Jan 05, 2018 -

A brief introduction to the stabilization mechanism of composite stabilizers

The thermal decomposition of PVC is the release of HCl from the heat sensitive part and the formation of double bonds in the PVC structure. Because of the high activity of propylene chloride, the reaction can proceed continuously, and continue to form conjugated double bonds, which become the structure of polyolefin and cause the coloring of products.

When calcium and zinc stabilizers are combined, first of all, the zinc soap is accompanied by the substitution of acroleyl chloride, accompanied by a double bond transfer. The polyene structure was destroyed and discoloration was inhibited. However, zinc chloride will precipitate in the PVC, the catalytic effect of HCl removal, the PVC is not stable, even caused by bridging blackening. Calcium soap then regenerated zinc chloride from zinc soap and stable chlorine atoms in PVC to zinc soap through the metathesis reaction, so as to activate zinc soap on one hand, thus activating zinc soap on the one hand, and inhibiting the destruction of zinc chloride on the other hand. A large number of organic compounds can greatly improve the initial coloring of products, so it is also used in stabilizers to make up for the deficiency of the early coloring of calcium and zinc stabilizers.

Polyols are also used in PVC calcium and zinc stabilizers. The polyol is used by chelating metal chloride to suppress deterioration in addition, polyols can also in metal salt under the catalysis of replacement of propenyl, initial coloring improved calcium zinc stabilizer is also has a good effect, but the pressure of serious affects the application of polyol with polyols by application in the limit of PVC products in high insulation requirements.

Acid absorbents can be used as auxiliary stabilizers for PVC. It is speculated that they can form complexes at the reaction sites, reduce the activity of the reaction sites, and also capture HCl with catalytic activity, so that the reaction of HCl removal can be avoided. The epoxides are often used with calcium and zinc stabilizers and have a certain synergistic effect.

In a word, composite heat stabilizers are beneficial to scale production and provide a new direction for the development of lead salt heat stabilizers. An important index of the composite lead salt stabilizer is the content of lead. The lead content of the composite lead salt stabilizer is generally 20%-60% at present, and the 3.5-6 dosage is used in the production of PVC plastic door and window profiles.